With the recent rapid spread of electronic devices in various fields, including homes and offices, an electromagnetic interference such that an electromagnetic wave leaking from a certain electronic device causes malfunction of another electronic device, is now posing a problem. To prevent such an inconvenience, various electromagnetic wave shielding materials are in use.
Moreover, under the Product Liability Law (PL Law), not only electronic devices but also electromagnetic wave shielding materials are required to be flame-retardant. Above all, a demand for such flame retardancy as satisfies FMVSS Standard and UL Standard is strong.
As an example of an electromagnetic wave shielding material, mention may be made of fiber cloths having metal-coated fiber surfaces. In many of those fiber cloths, the coating metals serve as oxidation catalysts and enhance the combustibility. This is presumed to be because not only the metal coatings obstructs a fire extinguishing action induced by melting of fibers but also the thermal conductivity of fibers is improved and promotes the spread of fire. Various studies have been made for improving the flame retardancy of such metal-coated fiber cloths.
In JP 62-21870A there is disclosed a metal-deposited flameproofing fiber wherein a phosphorus compound-based antiflaming agent and a halogen compound-based antiflaming agent are applied in combination to a metal-deposited fiber to improve the flameproofness synergistically. In recent years, however, attention has been paid to the relation between halogen compounds and dioxins. The structures of halogen compounds-based antiflaming agents are closely similar to the structures of dioxins, and it is said that if halogen compounds are burned together with such metal elements as copper and iron at temperatures in the range from 300 to 600° C., dioxins may be produced, and even if they are burned and decomposed at a temperature of 800° C. or higher for the purpose of perfect combustion, dioxins are produced as the temperature drops. In these points, i.e., from the standpoint of environmental pollution, the use of halogen compounds-based antiflaming agents is not preferable.
In JP 7-42079A it is disclosed that the surface of a metal-coated fiber cloth is coated with a urethane resin, then the surface of the urethane resin is coated with a mixture of an organic compound antiflaming agent such as an organophosphorus compound and an inorganic compound antiflaming aid such as an antimony compound, and further the surface of the mixture is coated with a urethane resin, to afford a metal-coated fiber cloth having flameproofness and a rust preventing effect. However, the antimony compound used as the antiflaming aid is poisonous to the human body and is therefore not desirable.
Thus, attention has recently been paid to safety for the environment and the human body, and in order to meet such safety, the development of a flame-retardant metal-coated cloth not using a halogen compound or an antimony compound is desired.
For example, the use of magnesium hydroxide and aluminium hydroxide as a substitute for the halogen compound and the antimony compound has been proposed. However, even if these compounds are applied each alone to cloth, a satisfactory flame retardancy is not obtained, and if they are each used in a large quantity for improving the flame retardancy, the feeling of the cloth becomes hard.
The use of phosphorus compounds such as red phosphorus and phosphoric esters has also been proposed. However, red phosphorus produces phosphine and thus involves the problem of toxicity, and phosphoric esters are generally low in phosphorus content and do not afford a satisfactory flame retardancy.